In recent years, advances in medical electronics and in other areas where electronic control is used have created a need for pneumatic and hydraulic mechanisms that are compatible with electronic circuitry. Because medical electronic devices are usually used in the treatment of one patient at a time, the volume of air or fluid required in the treatment usually is not large so that the pneumatic and hydraulic valve mechanisms can be of relatively small size. The speed capability of electronic circuitry, furthermore, requires pneumatic and hydraulic mechanisms that can act more quickly than the large and bulky mechanisms that are now commonly employed.